This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We propose to use small-angle x-ray scattering to investigate substrate-induced conformational change of lysine 5,6-aminomutase (5,6-LAM). 5,6-LAM is an adenosylcobalamin (AdoCbl, or coenzyme B12)- and pyridoxal 5[unreadable]-phosphate (PLP, coenzyme B6)-dependent alpha2beta2 tetramer that catalyzes an unusual, reversible, 1,2-rearrangement of the terminal amino group of D- or L-lysine and of L-beta-lysine. AdoCbl is an important cofactor in free radical chemistry reactions. The crystal structure of the apo-5,6-LAM suggests that substrate binding likely induces a large conformational change to place AdoCbl close to both the substrate and PLP in the active site. We propose to use SAXS to examine (i) the role(s) of cofactors;(ii) the proposed substrate-induced conformational change;and (iii) the function-structure relationship of 5,6-LAM by correlating catalytic activity, substrate specificity, and the proposed conformational change. In addition, a highly disordered region connecting the dimerization and catalytic domains of 5,6-LAM is revealed by the crystal structure, and the role(s) of the highly disordered region and the dimerization domain in the proposed conformational change and in the catalytic activity/substrate specificity of the enzyme will be investigated.